KTM 300 not shifting into 6th gear

Hi, I have a 6 speed KTM 300 xc-w. It shifts through all the gears just fine but when I try to shift up into 6th its like it doesnt exist. I click up and it feels like im out gears but it should be shifting into 6th. Any one ever encounter this before or know where I should start looking?

Was motor ever swapped out . 6 speed came out in 2011. What year is your bike ?